I've decided to go with a UK rebuild from Chambers Rotary Specialist.
Although it says 12 months 10,000miles warranty in the notes below, by addressing some of the known issues at the same time such as replacing the ignition coils (having D585 ignition coils) and installing the SORN Oil kit I was able to get a 3 year 30,000miles warranty (provided I do the recommended oil change etc and not use it on the track etc).
My main reason for choosing this tuner garage was because I could almost always get the shop owner on the phone and discuss things with him.
I want to let you know how it goes as I accumulate the miles 
HALF BRIDGE PORTED RX8 231 REBUILT ENGINE : Price: £ 1,550.00
Mazda RX8 231 Half Bridge Ported Engine + Racing Beats Street Port 
Half Bridge Ported
Half Bridge & Housing description Mazda RX8 13B MSP 6 Port High Power Refurbished engine with Half Bridgeport and street ported using the racing beats template.
rebuild content:
- O-ring gasket set
- Apex seals
- Apex Seals Springs
- Corner Springs
- Side Seal Springs
- Rotor O-ring Oil Seals
- Rear & Front E-Shaft Oil Seals
- Rear Stationary Gear O-ring
- Upgraded E-Shaft Oil Flow Pellet
- Front & Rear Stationary Gear Bearings
- Rotor & Springs Decarb & Deep Clean
Notes:
- Additional items may be required depending on the condition of the original component.
- 12 months or 10,000 warranty on this engine. if used for track then has additional limitations.
- The old engine block is expected to return to new engine. additional £ 190.00 charge for no exchange of engine.
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Chambers Rotary Specialist
Unit 2
Finchwood Farm
Copse Lane
PO11 0QB
Tel: 02392 466395
